This invention has particular application to sinkers for underwater use, such as those used for fishing lines and as weights for diving belts and the like. Such weights and sinkers will hereinafter be referred to collectively as sinkers.
Large quantities of lead are used to manufacture sinkers, especially for fishing lines and nets and the like and for diver""s weight belts. Sinkers are mostly formed from lead which is toxic and are often manipulated by hand and thus they expose many persons, and especially young persons, to potential contamination from the lead from which they are formed. Furthermore, many sinkers, and particularly fishing line sinkers are lost during use and litter the beds of fish habitats. This constitutes a significant contamination of fish habitats which is difficult to remove or reduce.
The present invention aims to alleviate at least one of the above disadvantages and to provide sinkers and methods of manufacturing sinkers which will be efficient in use.
With the foregoing in view, this invention in one aspect resides broadly in a sinker having a non-toxic metal body provided with a line passageway therethrough and a non-toxic barrier material coating all surfaces of the sinker body whereby the body material is isolated from interaction with the surrounding atmosphere or water.
The sinker bodies are preferably formed from steel and may be formed by being supplied as cylindrical steel billets fed randomly to a forge in which the billet is forged between heads having part-spherical cavities into a substantially spherical shape and finished with a passageway therethrough. Alternatively the sinker bodies may be cast from steel or iron or folded or formed from blanks about a mandrel or in such a manner that a line passageway remains through the formed body.
Preferably the body is formed from non-toxic metal powder which may be ferrous or non-ferrous metal powder. Advantageously, the body is formed from a non-toxic magnetic material so that lost sinkers, especially in an underwater environment in a localised fish habitat, may be readily recovered by scanning with a suitable magnet to recover the sinkers.
In the preferred form the body is formed from compressed iron powder and more preferably iron powder which contains a lubricant such as zinc stearate and which is sintered to at least some extent to increase its resistance to breakage due to impact. Suitably the iron powder is compressed at a pressure of about forty-five tons per square inch, providing a decrease in volume of the iron powder of about two and one-half times.
Suitably the compressed powder metal body is formed in a cylindrical passage in a die into and/or through which opposed punches move to compress a measured quantity of metal powder therebetween.
Preferably one punch supports a reciprocable pin about which the metal powder is compressed and the opposing punches are moveable through the die after the pressing process to remove the compressed body from the cylindrical passage. Thereafter the pin is withdrawn into its supporting punch to dislodge and discharge the compressed body therefrom
It is also preferred that the compressed powder metal body discharged from the compression means be sintered in an oven for increasing the strength of the body. The body may be sintered in known manner at high temperatures in the order of 1100xc2x0 C. in an oven in the presence of an inert gas such as nitrogen which flows through the oven.
Preferably however where the metal powder is iron powder, the sintering process is performed as a low temperature process in which the temperature in the oven is maintained below that which will cause visible oxidisation of the body such that the presence of an inert gas is not required. This also enables a relatively low cost bell-type oven to be utilised.
Preferably the sintering process is performed in the range of 350xc2x0 C. to 800xc2x0 C. for about thirty minutes so that the sintered body is generally capable of withstanding a throw-down test onto a concrete floor. Bodies tested in this manner prior to the sintering process mostly fail and shatter.
It is further preferred that the barrier material is a non-metallic coating material which is inert in its intended environment. However the coating may be an electroplated coating.
The barrier material is preferably a coating applied to the body in liquid form or spray form but it may be applied in powder form and bonded thereto. The barrier material is suitably a polymer coating which when cured exhibits properties of chemical resistance and toughness. It may be a polyurethane resin coating or water reducible one or two pack polyurethane coating or a combination thereof.
The barrier material may be applied in a process such as that described in our co-pending International patent application No. PCT/AU96/00775 or it may be applied as described below.
Preferably the coating material is suitable for application directly to the body but if desired it may be applied to a primed body primed with a compatible primer. A preferred barrier coating is an epoxy resin coating applied to the sinker body. The epoxy resin coating may be a water reducible coating or a conventional two-part epoxy resin coating.
Preferably the coating for the line passage is less resistant to degradation in an underwater environment than the coating on the outer surface of the body such that in time the passage coating will degrade and expose the metal body to the degrading effects of an underwater environment, especially a saltwater environment.
For this purpose the line passage is preferably coated with a water reducible paint such as a water reducible epoxy resin and the outer surface of the body is coated with a conventional two-part epoxy resin This provides a tougher outer surface to withstand abrasion and impact from which the line passage is shielded. Thus a long shelf life may be achieved together with a reduced underwater life.
In a further aspect it is preferred that the sinker adapted for use with fishing line be coated with a coloured or a selection of barrier material colours which is selected for either camouflaging the presence of a sinker In an underwater fish habitat or for providing a fish attractant. As a fish attractant, the barrier material may include metal flakes or like particles of a distinctly different colour to the base coating which sparkle or reflect light. The base coating may also be a multi coloured coating.
In yet a further aspect this invention resides broadly in a method of providing a barrier coating over the surfaces of a plurality of sinkers each having a line passageway therethrough, the method including:
submerging the sinker in a bath of coating liquid able to flow into and coat the line passageway;
withdrawing the sinker to a cleaning station at which the coating liquid is substantially removed from the external surface of the sinker;
arranging the sinkers in spaced apart relationship on a conveyor;
painting the portions of the sinker exposed above the conveyor with a barrier coating and causing the coating to harden;
rolling the sinkers along on said conveyor to a position at which the sinkers are supported on the conveyor on their painted side;
painting the newly exposed portions of the sinker with a barrier coating and causing the coating to harden.
Preferably the painting operations are performed automatically at separate spray paint stations and the sinkers are transported to the spray paint stations on the conveyor. It is also preferred that the sinkers be fed randomly from the cleaning station to location means at which the location means provides separate locating positions in space apart relationship for receiving individual sinkers and being disposed above the conveyor, and the location means is operable to deposit the located sinkers onto the conveyor in aligned closely spaced rows of sinkers.
Preferably the painting operations are performed automatically at separate spray paint stations and the sinkers are transported to the spray paint stations on said conveyor.
It is further preferred that the conveyor assembly is a belt type conveyor having a consumable layer of sticky faced material, such as automotive fire rated masking tape, which receives sinkers in the pattern formed by the primary location means and positively holds the sinkers In that pattern. When supported on this layer the freshly part painted sinkers may be passed through a heating zone for quick hardening of the paint.
Suitably the pattern has the sinkers arranged in staggered rows whereby a minimum space of about 2 mm may be maintained between adjacent sinkers. This allows the upper surface of the sinkers to be spray painted without concern for the sinkers moving and contacting one another.
It is further preferred that in the rolling process all but the leading or trailing row of sinkers are rolled along the sticky faced material onto the unpainted sticky space previously occupied by another adjacent sinker whereby they are again positively located in spaced apart relationship for
further treatment painting.